Method and device for producing a large-volume container

ABSTRACT

The invention relates to a method for producing a large-volume cup-shaped or tub-shaped container made of a synthetic thermoplastic material, whereby a compact plastic, flexible hose-type preform ( 6 ) is extruded to obtain a given length and the container ( 1 ) is subsequently shaped. In order to carry out said operations with the aid of extremely simple extrusion devices and moulds, thc extruded preform ( 6 ) is expanded to a given size and a core ( 2 ) is moved upwards into the expanded preform ( 6 ). The lower, open end of the expanded preform ( 6 ) is then clamped against the core ( 2 ) to provide a seal and the preform is shaped by air in order to form a container.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for producing a large-volume,cup-shaped or tub-shaped container of thermoplastic material, wherein ahose-shaped pre-form of compact plastic material is extruded to apredetermined length, is widened by means of spreading elements to apredetermined size, and subsequently formed by forming air to thecontainer, as well as to a device for performing the method.

2. Description of the Related Art

Transport and storage containers of compact plastic material, which arecup-shaped or tub-shaped, i.e., open at the top, are known which areinitially produced by an extrusion method, in which a hose-shapedpre-form is produced, and a subsequent blowing method in a hollow, atleast two-part mold, in which the hose-shaped pre-form is widened byblowing air and brought into contact with the inner wall of the hollowmold. The thus shaped container is then still closed at the top. Bycutting off the upper cover area, the required container open at the topis then produced. This cutting step represents an additional workingstep which requires a special cutting device. Moreover, the upper edgeof the container has a relatively minimal strength which isdisadvantageous when the container is used as a protective container foranother container.

A protective container for a large-volume container is known by whichthe aforementioned disadvantages are avoided.

This protective container has, however, a wall which is comprised ofthree layers wherein the inner layer is formed of a foamable plasticmaterial. Such a wall, on the one hand, entails a high materialconsumption and requires, on the other hand, an extrusion device withrelatively high capital investment. In addition to the extrusion devicea mold is required which is complex and comprised of an inner mold andan outer mold and must withstand the foaming pressure of the innerlayer. The method, as already mentioned above, can be performed onlywith a foamable inner layer. From a U.S. Pat. No. 5,474,734, a methodfor manufacturing hollow mold parts of thermoplastic material by ablowing process is known in which the finished mold parts are to havedifferent wall thicknesses. In order to achieve this, two spreadingelements, which can be supplied with a cooling liquid, are introducedfrom below into an extruded, hose-shaped pre-form with constant wallthickness and are moved apart. This reduces the wall thickness of thehose-shaped pre-form in the two areas which are not resting against thetwo spreading elements while the wall thickness remains constant in thearea where the hose-shaped pre-form rests against the cooled spreadingelement. As soon as the desired degree of spreading has been reached,the two spreading elements are removed from the pre-form. Subsequently,a two-part blowing mold is closed about the pre-form and its lower andupper ends are squeezed together. When closing the mold, a blowing spikeis introduced into the pre-form by means of which the pre-form is thenblown to the finished, closed molded part.

SUMMARY OF THE INVENTION

The invention has thus the object to provide a method for producing alarge-volume, cup-shaped or tub-shaped container of thermoplasticmaterial which can be performed with an extremely simple extrusiondevice and molds.

As a solution to this object it is suggested according to the inventionfor the method of the aforementioned kind that a core is moved into theextruded, hose-shaped and widened pre-form from below and the lower freeend of the widened pre-form is clamped sealingly against the core.

Such a method does not require a complicated and complex extrusiondevice for producing a large-volume, cup-shaped or tub-shaped containerthat is open at the top and has a wall of compact plastic material. Thepart of the mold which determines the final shape of the container canbe of a simple design wherein in many cases a core as a shaping body isalready sufficient. A special mold of at least two parts is then nolonger needed. When manufacturing the container on a core, blowing airis exclusively used as the forming air. In the process of manufacturingin a mold, the forming air can be blowing air as well as a vacuum.

The invention will be explained in the following in more detail with theaid of embodiments illustrated in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

It is shown in:

FIG. 1 a plan view onto a core serving as a shaping body for performingthe inventive method,

FIGS. 2 to 6 the individual method steps for producing a container, and

FIG. 7 a variation of a method step.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the FIGS. 6 and 7 of the drawing, a container 1, produced indifferent ways, respectively, is shown in section in a very simplisticillustration. This container 1 can have specially designed ribs in thearea of its lateral walls as well as can be we provided in the area ofits bottom, which here is at the top, with specially shaped ribs whichform a type of pallet-like bottom for the container. This container 1,which is formed in this connection of compact thermoplastic material, iscompletely open at its lower end according to FIGS. 6 and 7 so that thecontainer has a cup-shaped or tub-shaped configuration which is thenopen at the top for its later use.

The container 1 according to FIG. 6 is now produced by means of a core 2which is illustrated in a plan view in the FIG. 1 of the drawing. Thiscore 2, acting as a shaping body, has an approximately rectangularcross-section and is provided on all four corners with a respectivespreading element 3 complementing the cross-section of the core 2,respectively, but movable independently of the core. The spreadingelements 3 form a so-called spreading unit. Each spreading element 3 issupported by a pivot lever 4, only schematically illustrated, which ispivotable below the core 2 about axis 5. Two adjacently positioned pivotlevers 4 with their spreading elements 3 are correlated with a commonpivot axis 5. For the movement of the pivot levers 4 and thus of thespreading elements 3, drives, not illustrated in the drawing but knownin the art, are correlated therewith by which the pivot levers 4 andthus the spreading elements 3 can be moved from their position on thecorners of the core 2 inwardly into the position illustrated in FIG. 1,and back. In addition, each axis 5 has a lifting drive, not illustratedbut known in the art, correlated therewith by which the pivot lever 4and thus the spreading elements 3 can be lifted into a predeterminedposition which will be explained in the following. If needed, both axes5 can have one common lifting drive correlated therewith. Also, the core2 can be lifted by means of a lifting drive. In this connection, thelifting drives are, for example, mounted on a common frame.

For the manufacture of the container 1 according to FIG. 6 it is nowassumed that the core 2 is lowered and the spreading elements 3 haveassumed their inner position within but above the core 2. This meansthat the spreading elements 3 are pivotable inwardly by means of theirpivot arms 4 and now assume their inner position. In this position ofthe spreading elements 3, a hose-shaped pre-form 6 is now continuouslyor discontinuously moved from above by means of an extruder, notillustrated, about the inwardly moved spreading elements 3, asillustrated in FIG. 2. This hose-shaped pre-form 6 has, for example, asingle-layer wall of compact plastic material. The pre-form 6 is nowextruded in a predetermined length illustrated in FIG. 2 about theinwardly moved spreading elements 3. In this connection, the fourspreading elements 3 are surrounded by the hose-shaped pre-form 6. Assoon as the pre-form 6 has the required length, it is then squeezedtogether by blades 7, only schematically shown, or a so-called hoseclosure and welded (FIG. 3). Now the spreading elements 3 are movedoutwardly by means of their pivot arms 4 to such an extent that thehose-shaped pre-form 6 is widened. The degree of spreading ispredetermined to be so large that the core 2 can be moved into thewidened pre-form 6 according to FIG. 4. This means that the core 2 islifted. By means of special clamping elements 8 the extruded pre-form 6is now pressed in the area of its lower open end against the core 2 sothat an extremely narrow squeezed rim 9 is produced, as illustrated onan enlarged scale in FIG. 6 of the drawing.

The core 2 is now provided at its surface with relatively small channels11 which open into a central channel. This central channel is connectedto a vacuum line. By means of forming air, in this case it is theapplication of vacuum to the channels 11, the wall of the pre-form 6 isnow brought into contact at the surface of the core 2. Accordingly, thecontainer 1 of FIG. 6 is formed. After cooling and hardening of thecontainer 1, the core 2 can be removed therefrom and the extremely thinsqueezed rim 9 can be cut by means of a knife.

In the described method the container 1 is produced without using anouter mold. This means, however, that the thickness of the wall of thecontainer 1 does not necessarily have a uniform thickness everywhere.With a corresponding control of the extrusion process it is now possibleto form the thickness of the wall of the hose-shaped, extruded pre-form6 differently so that the wall of the finished container 1 in theindividual areas of its height can also be different. For the removal ofthe core 2 from the container 1, it is now required to hold thecontainer 1 on a stripper bar and to move the core 2 together with thespreading elements 3 again into the initial position. The container 1 isnow completely free and can be removed from the device.

In the manufacture of the container 1 of FIG. 7, the shape of thecontainer 1 is not only determined by the core 2 but by a two-part outermold 10. The core 2 accordingly can be designed considerably shorter.The short core 2 with the pre-form 6 according to FIG. 5 is moved intothe outer mold 10 and is clamped therein by means of clamping elements 8on the core 2. This results also in a squeezed rim 9. After closing thehollow mold 10 about the core 2, blowing air as shaping air isintroduced through the core 2 into the hose-shaped pre-form 6 whichcauses the hose-shaped pre-form 6 to contact the inner wall of thehollow mold 10. After cooling of the container 1, the squeezed rim 9 isagain cut by a knife and the hollow mold 10 as well as the core 2 areremoved.

In a variation of the explained embodiments, it is possible to use onlytwo, three or more than four spreading elements 3. In the case of twospreading elements 3 they must be shell-shaped and can be hinged orfoldable. The cross-section of the spreading elements 3 can otherwise beas desired. It is decisive in this connection that the spreadingelements 3 are able to widen the pre-form 6, which is smaller incross-section, or to enlarge its peripheral contour such that a core 2can be introduced whose cross-section is greater than the originalcross-section of the extruded pre-form 6. Moreover, it is possible todesign the core 2 itself to be collapsible so that the spreadingelements 3 can be eliminated and the core 2 forms the so-calledspreading unit.

What is claimed is:
 1. A method for producing a large-volume, cup-shapedor tub-shaped container of thermoplastic material, the methodcomprising: extruding a hose-shaped pre-form of compact plastic materialto a predetermined length, initially widening the extruded pre-form by apredetermined amount, subsequently moving a core from below into thewidened pre-form, subsequently clamping the widened pre-form at a lowerfree end thereof sealingly against the core, such that an opening of thecontainer is formed, wherein an area of the opening approximately isequal to a cross-sectional area of the container, subsequently shapingthe pre-form by means of shaping air into the container, and clampingthe pre-form by means of clamping elements at the core so as to form asqueezed rim at the pre-from.
 2. A method for producing a large-volume,cup-shaped or tub-shaped container of thermoplastic material, the methodcomprising: extruding a hose-shaped pre-form of compact plastic materialto a predetermined length, initially widening the extruded pre-form by apredetermined amount, subsequently moving a core from below into thewidened pre-form, subsequently clamping the widened pre-form at a lowerfree end thereof sealingly against the core, such that an opening of thecontainer is formed, wherein an area of the opening approximately isequal to a cross-sectional area of the container, subsequently shapingthe pre-form by means of shaping air into the container, wherein thecore is configured as a shaping body, further comprising forming thecontainer by means of a vacuum on the core.
 3. The method according toclaim 1, wherein the core is configured as a shaping body, furthercomprising forming the container by means of a vacuum or blowing air ona two-part hollow mold surrounding the core at a spacing.
 4. The methodaccording to claim 1, further comprising widening the extruded pre-formby at least two rod-shaped spreading elements.
 5. A method for producinga large-volume, cup-shaped or tub-shaped container of thermoplasticmaterial, the method comprising: extruding a hose-shaped pre-form ofcompact plastic material to a predetermined length, initially wideningthe extruded pre-form by a predetermined amount, subsequently moving acore from below into the widened pre-form, subsequently clamping thewidened pre-form at a lower free end thereof sealingly against the core,such that an opening of the container is formed, wherein an area of theopening approximately is equal to a cross-sectional area of thecontainer, subsequently shaping the pre-form by means of shaping airinto the container, further comprising widening the extruded pre-form bythe core.
 6. A device for producing a large-volume, cup-shaped ortub-shaped container of thermoplastic material, the device comprising anextrusion head for forming a hose-shaped pre-form of a single-layercompact plastic material, a spreading unit mounted below the pre-formand movable from below into the pre-form by a relative movement, and acore movable from below into the pre-form after the pre-form has beenwidened by the spreading unit, wherein the core comprises at least onetwo-part clamping element, wherein the core can be loaded with a vacuum,and wherein the core is configured to form an opening of the container,wherein an area of the opening is approximately equal to across-sectional area of the container.
 7. The device according to claim6, wherein the spreading unit comprises at least two spreading elementsthat can be moved apart.
 8. The device according to claim 7, wherein thespreading elements have different cross-sectional shapes. 9.The deviceaccording to claim 7, wherein the spreading elements are formed of partsof the shaping body.
 10. The device according to claim 7, wherein thespreading elements are configured to be radially movable.
 11. The deviceaccording to claim 7, wherein the spreading elements are configured tobe pivotable.
 12. The device according to claim 6, wherein the spreadingunit is formed by a spreadable or foldable core.
 13. A device forproducing a large-volume, cup-shaped or tub-shaped container ofthermoplastic material, the device comprising an extrusion head forforming a hose-shaped pre-form of a single-layer compact plasticmaterial, a spreading unit mounted below the pre-form and movable frombelow into the pre-form by a relative movement, and a core movable frombelow into the pre-form after the pre-form has been widened by thespreading unit, wherein the core comprises at least one two-partclamping element and a hollow mold loadable with vacuum or blowing airand surrounding the core at a spacing, wherein the core is configured toform an opening of the container, wherein an area of the opening isapproximately equal to a cross-sectional area of the container.
 14. Thedevice according to claim 13, wherein the spreading unit comprises atleast two spreading elements that can be moved apart.
 15. The deviceaccording to claim 14, wherein the spreading elements have differentcross-sectional shapes.
 16. The device according to claim 14, whereinthe spreading elements are formed of parts of the shaping body.
 17. Thedevice according to claim 14, wherein the spreading elements areconfigured to be radially movable.
 18. The device according to claim 14,wherein the spreading elements are configured to be pivotable.
 19. Thedevice according to claim 13, wherein the spreading unit is formed by aspreadable or foldable core.
 20. The method according to claim 1,further comprising cutting the squeezed rim after cooling of thecontainer.